The present invention relates to a method for forming opaque quartz glass or silica glass components, more particularly, for forming and shaping fused quartz or fused silica glass into an opaque processing component of a desired shape and dimensions.
Quartz glass processing components, such as tubes, rods, panels, domes, plates, rings, and blocks, either as semi-finished or finished goods, are important components for heat engineering applications, in which good thermal insulation along with high temperature stability and thermal fatigue resistance are essential. Applications of the semiconductor industry, in particular, put ever increasing demands on the use of opaque quartz glass tubes and other components. These applications require the quartz glass components to be opaque, mainly in the infrared region of the wavelength spectrum, and also to be as pure as possible. However, these demands can be difficult to meet, as opacity and purity tend to be competing properties. More particularly, impurities present in the quartz glass actually contribute to the opacity of the glass, and thus opaque quartz glass typically has a low purity.
Impure opaque quartz glass is generally not suitable for use in applications such as those described above (i.e., the semiconductor industry) because of the significant negative effects of the impurities contained in the glass. Specifically, any contaminations present can cause contamination of the semiconductor wafers, devitrification of the quartz glass, resulting in brittleness and reduced thermal fatigue resistance of the quartz glass components formed therefrom. Also, quartz glass components fabricated from impure opaque quartz glass tend to have an inhomogeneous distribution of relatively large sized pores, which contributes only little to opacity, causes the density of the opaque quartz glass to be low, and reduces the mechanical stability and the serviceable life of the quartz glass component.
Thus, processes have been developed for forming a relatively pure and opaque quartz glass component using pure starting materials. Examples of high purity quartz glass can be found in U.S. Pat. Nos. 5,585,173; 5,674,792 and 5,736,206. Such processes typically begin with a preform or blank of an opaque and pure quartz glass. Such preforms are typically in the form of large blocks of quartz glass. However, it was found that, when the glass preforms were subjected to heating, such as in a thermal reforming process, the starting opaque glass becomes clear or transparent and loses its opacity. Such thermal reforming processes are described in various prior art references, such as Japanese Application Nos. 04026522 and 4485826; Japanese Application Publication Nos. 2004-149325 and 2005-145740; U.S. Pat. No. 7,832,234; and U.S. Application Publication No. 2010/0107694. However, none of these references are directed to thermal reforming of opaque and pure quartz glass. U.S. Patent No. 2002/0134108 does describe a thermal reforming process for opaque quartz glass, but the glass is a synthetic quartz glass.
The loss of opacity of the starting opaque and pure quartz glass, when subjected to thermal reforming, is particularly problematic for the formation of thin-walled opaque components, such as quartz glass tubes or tube sections, since the block-shaped quartz glass preform must be subjected to significant thermal reforming to achieve the desired tubular shape and low wall thickness. Accordingly, such thermal reforming processes have generally been avoided when the starting preform is made of pure and opaque quartz glass.
Instead, opaque quartz glass components (such as tubes and tube sections) are conventionally formed by starting with a preform of opaque and pure quartz glass and then mechanically machining the glass preform into the desired shape to form an opaque quartz glass component. Such mechanical machining processes include, for example, grinding, polishing, machining, core drilling, ultrasonic milling, laser cutting, or the like of the glass preform until the desired shape and dimensions are achieved. However, depending on the quartz glass component being made, a significant portion of the pure quartz glass of the starting preform may be wasted as a result of the mechanical treatment. For example, when making a ring or a short tube, such as for a semiconductor processing tube, typically only approximately 15% of the quartz glass of the starting preform is actually utilized in the opaque quartz glass component (i.e., the ring). The remaining 85% of the expensive opaque pure quartz glass is simply wasted. Thus, conventional mechanical machining processes for forming pure and opaque quartz glass components are costly and generally inefficient.
Accordingly, it would be desirable to provide a method and system for forming components made of a high purity and high opacity quartz glass in a cost-effective manner.
More particularly, it would be beneficial to provide simplified, efficient and cost-effective systems and methods for forming opaque and pure fused quartz glass into components, such as domes, tubes, tubular sections, plates, rods, panels, and rings for use in the semiconductor industry.